In radio communication systems, information (for example, voice, visual information, video information, SMS [Short Message Service] or other data) is transmitted by using electromagnetic waves via a radio interface between the sending and receiving station such as, for example, radio access devices and subscriber stations. Therefore, the transmission of electromagnetic waves is carried out with carrier frequencies, which lie in the frequency band provided for the specific system.
Usually, at least one radio access device and one device for radio access control (BSC, Base Station Controller) form part of a base station subsystem (RNS, Radio Network Subsystem or BSS, Base Station Subsystem). A radio communication system usually includes a plurality of base station subsystems, which are connected to a core network (CN, Core Network). In this case, the device for the radio access control of the base station subsystem is connected to an access device of the core network.
For the established GSM mobile radio system (Global System for Mobile Communication), frequencies of 900, 1800 and 1900 MHz are used. These systems essentially transmit voice, telefax and short messages as well as digital data.
Frequencies are provided in the frequency band of approximately 2000 MHz for future mobile radio systems with CDMA or TD/CDMA transmission methods such as, for example, UMTS (Universal Mobile Telecommunication System) or other systems of the third generation. These systems of the third generation are developed with a view to obtaining world-wide radio coverage, an extensive range of services for the transmission of data and especially a flexible management of the capacity of the radio interface, which in the case of radio communication systems is the interface with the least resources.
In the case of radio communication systems, subscriber stations accessing the common transmission medium are regulated by the multiple access methods/multiplex methods (Multiple Access, MA). In the case of these multiple accesses, the transmission medium can be divided between the subscriber stations in the time area (Time Division Multiple Access, TDMA), in the frequency area (Frequency Division Multiple Access, FDMA), in the code area (Code Division Multiple Access, CDMA) or in the space area (Space Division Multiple Access, SDMA). A combination of several such methods can also be used. In order to make it possible to deal cost-effectively with the scarce radio resources, devices that manage the radio resources or carry out a resource allocation are located in radio communication systems. In this case, the radio resource of a radio interface can for example be a time slot of a frequency pair or even only one of the two (time slot or frequency).
Different methods are known for addressing subscriber stations in radio communication systems. Besides unicasting in which precisely one subscriber station is addressed, broadcasting in which all the subscriber stations within the radio coverage area of the sending radio access device are addressed seems to be most commonly used. In addition, multicasting is known in which the subscriber stations of a multicast group are addressed at the same time as the transmission of multicast information. A multicast, in which the addressed group includes all the subscriber stations within the range of a radio access device, corresponds to a broadcast. For multicast services, it is required that the addressed subscriber stations belong to a limited group, while this is not the case for broadcast services.
As a result, besides individual useful information, useful information is also transmitted in radio communication systems, which is made available to a plurality of subscriber stations. Such useful information includes for example video streams, advertising texts, or general information such as traffic reports. The services for transmitting useful information, which are not only provided individually to a single subscriber, but are made available to a plurality of subscribers are covered by the term MBMS (Multimedia Broadcast/Multicast Service). The core network usually makes available the different MBMS services as separate data flows.
Before the useful information of one group of subscriber stations is transmitted, the subscriber stations are notified as to how many subscribers would like to use the service. This notification of the subscriber stations is necessary to make possible the configuration of the receivers. For the notification, group-specific mechanisms are usually used in which a plurality of subscriber stations is addressed at the same time.